Up until now, the fuel supply apparatus of this type for the internal combustion engine to be mounted on an automotive vehicle, comprises a fuel tank for reserving the fuel, a fuel pump for pumping the fuel from the fuel tank to supply the fuel to a fuel consumption unit, and a pressure controlling apparatus for adjusting the fuel supply pressure when the fuel is supplied to the fuel consumption unit by the fuel pump. The pressure controlling apparatus is adapted to adjust the fuel supply pressure to injectors forming part of the fuel consumption unit with the fuel pump for pumping up the fuel from the fuel tank.
The pressure controlling apparatus of this kind is generally provided with a housing, and a diaphragm having an adjustment valve at the central portion thereof and separating the housing into two chambers. The diaphragm has one surface side receiving the fuel pressure in one of the adjustment chambers to have the central portion deformed in the directions to close or open the adjustment valve in response to the fuel pressure varied, and the other surface side held in engagement with a compression coil spring to have the diaphragm suppressed from being deformed. The pressure controlling apparatus thus constructed is adapted to have the pressure adjustment valve held in the open state until the fuel pressure in the pressure adjustment chamber reaches the set pressure. Further, the pressure control apparatus is usually disposed in the fuel tank together with the fuel pump.
As a pressure controlling apparatus, there has so far been proposed a pressure controlling apparatus provided with a variable fuel pressure adjustment valve which comprises a diaphragm for dividing the inside of a housing into an adjustment chamber and a back pressure chamber, the adjustment chamber facing one surface side and having a fuel introduction port through which the pressurized fuel is introduced from the fuel pump, the back pressure chamber facing the other surface side and having a fuel discharge port through which the back pressure fluid is introduced, a plunger forming an open chamber open to the atmosphere between the diaphragm and the back pressure chamber, a valve member provided on the diaphragm to selectively open or close the discharge port in response to the deformation of the diaphragm, a spring intervening between the diaphragm and the plunger to urge the valve member in the direction to open or close the valve member, and a stop member for regulating the movement range of the plunger (for example see Patent Document 1).
The fuel supply apparatus disclosed in the Patent Document 1 is provided with the variable fuel pressure adjustment valve forming part of the pressure controlling apparatus thus constructed, so that supplying or not supplying the back pressure fluid causes the set load of the spring to be changed at two stages, thereby making it possible to change the set value of the fuel pressure to be adjusted into any one of the low side or the high side.
However, the fuel supply apparatus disclosed in the Patent Document 1 encounters such a problem that it is difficult to make the fuel supply apparatus small in size since the variable fuel pressure adjustment valve is required to have three chambers formed therein although the fuel pressure can be changed by only one variable fuel pressure adjustment valve. The known supply apparatus encounters another problem that the variable fuel pressure adjustment valve is required to be disposed within several limitations, resulting from the fact that the pipes for supplying the fuel to the pressure adjustment chamber and the back pressure chamber are forced to be connected in opposite directions with each other.
In addition, the control unit for controlling the fuel pressure is not designed in consideration of the time necessary for changing the fuel pressure. For this reason, there may cause some cases in which the fuel is injected during the fuel pressure change, and in which the target fuel pressure is differentiated from the real fuel pressure. As a result, the injection amount to each of the cylinders is not adequate, thereby causing another problem encountered by the conventional fuel supply apparatus that there is a possibility that the air-fuel ratio differs from the target air-fuel ratio.
In view of these problems, it is known as the fuel supply apparatus capable of changing the fuel pressure that the changing time for the fuel pressure is estimated (for example see Patent Document 2).
The fuel supply apparatus disclosed in the Patent Document 2 comprises two variable fuel pressure adjustment valves, electromagnet valves for changing the states of the variable fuel pressure adjustment valves, and an ECU for controlling the electromagnet valves. The fuel supply apparatus disclosed in the Patent Document 2 is different from the fuel supply apparatus disclosed in the Patent Document 1, but requires two variable fuel pressure adjustment valves for changing the fuel pressure, thereby making it impossible to solve the problem to downsize the fuel supply apparatus. However, the fuel supply apparatus disclosed in the Patent Document 1 can make the real air-fuel ratio near the target air-fuel ratio by having the ECU set the fuel injection amount to the cylinder in response to the fuel pressure. For changing the fuel pressure, the fuel supply apparatus is adapted to predict the change of the real fuel pressure based on the rotation number of the engine.